1. Field of the Invention
The present invention relates to a centerless grinding machine for grinding workpieces mainly by using a super abrasive grinding wheel and with an ultra precision grinding operation.
2. Description of the Prior Art
Typically a centerless grinding machine is comprised of a grinding wheel, a regulating wheel, and a blade which is disposed between the two wheels for supporting a workpiece, whereby the workpiece supported by the blade and regulating wheel is ground to a desired dimension by the grinding operation of the grinding wheel facing the regulating wheel.
In such a centerless grinding machine, the grinding wheel is fixed to the rotational spindle through a tapered flange and the like, and is rotatively driven by a pulley mounted on one end of the rotational spindle. Further, when the grinding wheel becomes worn out, the position of a table provided for the grinding wheel is compensated by the amount of the wear for the accurate grinding to be effected. The guide ways for the grinding wheel table are formed by a hydrodynamic guide or low friction rolling guide way, or hydrostatic guide way. Such a machine which is manufactured for general purposes may also be applied to the grinding operation by the super abrasive grinding wheel.
In a grinding operation, the machining accuracies and efficiencies for a workpiece is mainly affected by the degree of accuracies and rigidities of the workpiece support and drive system and that of the grinding wheel including its rotational spindle.
When a large dimensioned super abrasive grinding wheel is to be used in a centerless grinding machine, and it is necessary to true the grinding wheel with accuracy, a special trueing machine provided apart from the grinding machine has to be used. In removing from the trueing machine the grinding wheel which has been trued and mounting it again on the grinding machine, any changes in accuracies should not occur that would increase the peripheral run-out of the wheel due to the mounting error of the wheel assembly in its transfer. However, in the structure of the conventional grinding machine, it is not possible to achieve the accuracy of the grinding wheel which satisfies the requirement to perform an ultra precision grinding operation, when the grinding wheel or grinding wheel unit which has been trued outside of, or apart from, the grinding machine is mounted again on the grinding machine.
Furthermore, in order to control the workpiece dimension to a high accuracy, it is necessary to accurately control the position of the grinding wheel tables. When a hydrodynamic guideway is used for the guideway for positioning the table, the accurate positioning of the wheel table can not be accomplished due to the influence of frictional force. In the structure which makes use of a low friction guideway, such as a rolling guideway and the like, there is such a defect that chatter vibrations tend to occur because of a low rigidity in the guiding direction, and this guideway is not appropriate for a high precision and efficient grinding.